Constraints of the compactness of the isolated neutron stars via X-ray phase-resolved spectroscopy

TL;DR

This study models the X-ray emission of the isolated neutron star RBS 1223 using phase-resolved spectroscopy, constraining its surface properties, magnetic field, and gravitational redshift to better understand neutron star compactness.

Contribution

It introduces a combined spectral and phase-resolved modeling approach with a condensed iron surface and hydrogen atmosphere to derive physical and geometric properties of RBS 1223.

Findings

Surface temperatures ~105 eV and ~99 eV at the poles.

Magnetic field strengths ~8.6 x 10^13 G at the poles.

Gravitational redshift z ~ 0.16.

Abstract

A model with a condensed iron surface and partially ionized hydrogen-thin atmosphere allows us to fit simultaneously the observed general spectral shape and the broad absorption feature (observed at 0.3 keV) in different spin phases of the isolated neutron star RBS 1223. We constrain some physical properties of the X-ray emitting areas, i.e. the temperatures (Tpole1 ~ 105eV, Tpole2 ~99eV), magnetic field strengths Bpole1 ~ Bpole2 ~ 8.6x10^13G) at the poles, and their distribution parameters (a1 ~ 0.61, a2 ~ 0.29, indicating an absence of strong toroidal magnetic field component). In addition, we are able to place some constraints on the geometry of the emerging X-ray emission and the gravitational redshift (z ~0.16+0.03-0.01) of the isolated neutron star RBS 1223.